End switches in or for adjustable elements



Oct. 16, 1962 v R. e. DAWES 3,059,198

END swITcHEs IN OR FOR ADJUSTABLE ELEMENTS 2 Sheets-Sheet 1 Filed May 1, 1961 Oct. 16, 1962 R. e. DAWES 3,059,198

END SWITCHES IN OR FOR ADJUSTABLE ELEMENTS Filed May 1. 1961 2 Sheets-Sheet 2 United States Patent M 3,059,198 END SWITCHES IN OR FOR ADJUSTABLE ELEMENTS Reginald George Dawes, Swindon, England, assignor to The Plessey Company Limited, London, England, a

British company Filed May 1, 1961, Ser. No. 106,978 Claims priority, application Great Britain May 9, 1960 Claims. (Cl. 338163) This invention relates to adjustable electrical devices, in particular to adjustable resistors and potentiometers, and has for an object to provide an improved end switch of small space requirement for use in the adjustable elements or in connection therewith.

According to the invention the switch comprises an insulating plate member, rockable in its plane, which by a single-tooth type cam connection is coupled with the actuating element of the adjustable device so as to be moved from one position to the other and vice versa when the adjustable member enters and leaves, or passes, a predetermined end position in two opposite directions, a connection strip or its equivalent being provided in the plate member to interconnect a pair of fixed contacts in one, and break the said connection in the other position of the plate member.

An embodiment of the invention as applied to a rimoperated potentiometer is illustrated in the accompanying drawing, in which FIGURE 1 is a plan view with the cover panel removed,

FIGURE 2 is a section on line 22 of FIGURE 1.

The potentiometer comprises a base 10 which is moulded of insulating plastic and is provided at its centre with a boss 11, for example of bronze, by which an insulating cover panel 12 is held in spaced relation to the base 10. A moulded potentiometer track 13 is embedded in the base -10 concentrically with the boss '11, and it co-operates with a carbon brush 14 arranged in a brush carrier 15 of resilient plate metal. A tail '1-6 of the brush carrier 15 is lodged in a suitable recess of an annular setting member or rim -17 of insulating material, which is guided upon the base 10 and cover plate 12 by means of an annular shoulder 18 as shown in FIGURE 2. The boss 11 can be used as a terminal for establishing connections to the brush 1'4, and the two ends of the track 13 are provided with metal contacts 19 and 20, one of which may be used as further terminal, while the other is connected to one of two contact pins 3 and 4 moulded into the base, the heads of the contact pins 3 and 4 being slightly proud of the base. The other pin 4 serves as a third external connection.

To make and break connection between the pins 3 and 4 and thus cut the resistor track 13 into and out of circuit according to the position of the rim 17 and brush holder 15, a metal connecting strip is arranged flush with one surface of a plate-shaped nylon toggle 1 which, by means of a shoulder rivet 2, is secured to the base for pivotal movement, so that, due to the resilience of the toggle 1, the toggle surface which contains the strip 5, is held in yielding contact with the heads of pins 3 and 4. The rotatable rim 17 is provided at its inner side with a projection 6 arranged for co-operation with a recess 8 in the toggle member 1, so that when the rim 17 has been turned, in an anti-clockwise direction, to the position illustrated in FIGURE 1, the toggle member .1 will assume the illustrated position, in which the strip 5 is only in contact with pin 4 so that there is no electrical connection between pins 3 and 4, and the resistor track 13 is not in circuit. When the rim 17 is turned in a clockwise direction from the illustrated position to move brush 14 from its position near the end contact 20 towards the other end 3,059,198 Patented Oct. 16, 1962 contact 19 of the track 13, projection 6 co-operates with the recess in the toggle 1, to move the toggle to a second position which is the mirror image of its illustrated position in respect of the plane defined by the axes of pin 2 and of brush 11. In this second position the strip 5 interconnects the contact pins 3 and 4, thus completing the circuit of track 13. It will be appreciated that this switch movement takes place at the commencement of the rotation in the clockwise direction from the illustrated off position, and that the switch will then remain in the on position throughout any movement of the rim 17 beyond the end of the switch movement up to a point in which brush 14 reaches the other terminal 19 of the track 13 and also during reverse movement between the last-mentioned position and the point at which the switching-on movement had been completed. In order however to r duce the risk of accidental operation of the switch, for example as a result of mechanical vibrations, suitable retaining features may be incorporated in the device in a manner well known to those versed in the art. Thus the ends of contact strip 5 co-operating with the projecting heads of pins 3 and 4 may be lightly recessed, or an overcentre spring may be provided which opposes reversal of the switch from either of its end positions.

What I claim is:

1. A combined variable-resistor-and-switch device, comprising two substantially flat housing end plates spaced from each other, an annular housing wall interconnecting said end plates to form jointly therewith a hollow housing, a fiat, part-circular resistance track fixedly arranged in said housing on one of said end plates coaxially with said annular wall, a wiper arm mounted in said housing adjacent to the other end plate and having a wiper contact extending into contact with said track, said wiper arm and annular wall being jointly rotatable, relative to said one end plate, about the common axis of said track and annular wall, a pair of mutually insulated fixed contact elements on said one end plate, and a rocker plate parallel to said end plates and pivoted in said housing for movement between two end positions about an axis parallel to said common axis, the annular wall having an inwardly projecting tooth, and the rocker plate having a pair of teeth between which said tooth is adapted to engage, the pivot axis of the rocker plate being arranged between said teeth and the axis of the annular wall so as to permit said tooth of the wall to pass over one of the rocker teeth to engage the other rocker tooth and move the rocker plate to one of its end positions, in which the tooth of the wall element can pass over the other rocker tooth, when said annular wall is rotated in one direction but will strike the firstmentioned rocker tooth and move the rocker plate to its other end position when said wall is rotated in the opposite direction, said rocker plate having a contact portion which in one end position of the rocker plate interconnects said fixed contacts and in the other end position of the rocker plate is clear of at least one of said fixed contacts, and the pivot axis of the rocker plate being arranged in a plane extending radially from the axis of the annular wall through the gap between the two ends of the part circular track to clear the Wiper contact throughout the wiping movement of the contact along the track.

2. A combination as claimed in claim 1, wherein the rocker plate is arranged between the housing and plate carrying the track and a portion of the Wiper arm situated between the wiper contact and the common axis of the track and annular Wall.

References Cited in the file of this patent UNITED STATES PATENTS 

